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Karyotypes

Karyotypes. IB1 Biology Song Hee Bae. Karyotypes. Karyotype: the number and appearance of the chromosomes in an organism. Karyotype is always found in a photograph of the chromosomes found in a cell arranged according to a standard format.

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Karyotypes

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  1. Karyotypes IB1 Biology Song Hee Bae

  2. Karyotypes • Karyotype: the number and appearance of the chromosomes in an organism. • Karyotype is always found in a photograph of the chromosomes found in a cell arranged according to a standard format. • Organisms that are same species usually have the same karyotype. • Can detect: • Gender • Chromosome abnormalities

  3. Karyotyping • Fetal cells obtained • Cells are stimulated to divide by mitosis. • Stops mitosis in stage of metaphase, because chromosomes are mostly visible in metaphase. • Chromosomes in the photograph are cut out and arranged into pairs according to their size and structure. • Two Methods of Karyotyping • Amniocentesis: a sample of amniotic fluid is removed from the amniotic sac around the fetus. • Chorionic villus sampling: obtaining a tissue sample from the placenta’s finger-like projections into the uterus wall.

  4. Examining Karyotypes Gender • Sex chromosomes. • XX – female • XY - male • Women - X chromosomes • Men - either X or Y chromosomes Chromosome disabilities • sometimes, chromosomes do not split during meiosis - non-disjunction. • Gametes are produced with either specific chromosome too many or too few. • Gametes with one chromosome too few usually quickly die. • Gametes with one chromosome too many sometimes survive. = down syndrome

  5. Down Syndrome • 47 Chromosomes in total • Three chromosomes of type 21, rather than two. • Can be due either to non-disjunction during the formation of the sperm or egg. • Can’t deduce the extent of affect. • The chance of down syndrome increases with the age of the parents.

  6. Vocabulary • Karyotype: the number and appearance of the chromosomes in an organism. • Karyotyping: the process of cutting the chromosomes in the photograph and arranging into pairs. • Amniocentesis: a method of extracting fetus cell by removing a sample of amniotic fluid from the amniotic sac around the fetus, using a hypodermic needle. • Chorionic villus sampling: a method of extracting fetus cell by obtaining a tissue sample from the placenta’s finger-like projections into the uterus wall. • Non-disjunction: non-separation of chromosomes.

  7. Reference • IB Biology Study Guides (page 25) • Pearson Biology (page 97) • Human Karyotype image linked • Mitotic metaphase image linked • Sex chromosome image linked • Down Syndrome Karyotype image linked

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